This disclosure relates to a damper assembly and specifically a multi-stage switchable inertia track assembly. More particularly, the multi-stage switchable inertia track assembly contains both a low frequency inertia track and a high frequency inertia track. The low frequency track is used to create damping to address vehicle smooth road shake. The high frequency track is used to create a high frequency sympathetic resonance to reduce transmission of idle disturbance frequencies from the powertrain to a vehicle body or frame. Selected features may find application in other related environments and applications.
The basic technology for switchable hydraulic engine mounts has been known in the industry for several years. Physical switching of a hydraulic mount from a fluid damped state to a non-damped state by way of opening and closing a port is well understood. However, there are multiple methods by which this can be achieved.
Most vacuum actuated hardware is mounted externally for ease of manufacture. This external mounting tends to reduce the efficiency of the mount response, but it does allow for easier sealing of the hydraulic fluid in the mount assembly. A problem with most conventional designs is that they use a diaphragm that encloses a volume and forms an air spring under the diaphragm and attached to an external port. Opening and closing this external port is the method used to “switch” the mount state, i.e., the stiffness or damping response. In the switch “open” state, air can be pumped to atmosphere from the volume. For example, the hydraulic engine mount has a low bearing spring stiffness with the open switch (the volume is open to atmosphere) and the engine mount damps or insulates idling vibrations (low amplitude, high frequency). In the switch “closed” state, the air in the volume acts as a stiff spring because the volume is closed or sealed and the damping fluid is transferred back and forth between a first or working fluid chamber and a second or compensating fluid chamber to damp high amplitude, low frequency vibrations. The air spring (closed volume) created by the closed port reduces the pressure of the fluid that would otherwise be pumped through the inertia track, as some of the fluid pressure is used to compress the air spring.
Other designs also use a vacuum actuated diaphragm that seals on the diaphragm cover and uses the diaphragm as a seal on the inertia track.
Still other designs use a rotary valve to open and close the port. These rotary valves can rotate either axially or radially with the mount. In either case, sealing of the valve can become an issue, where it is difficult to seal from either the low pressure side of the mount to high or from the high pressure side of the mount to atmosphere.
As with most switchable hydraulic engine mounts this mount is intended to suspend the powertrain, provide damping to powertrain motion, control the powertrain travel, and isolate the powertrain from the vehicle chassis. The switch mechanisms in multi-state mounts allow the mount to switch between four states. Two of the states allow the fluid effect of the mount to be decoupled from compliance vibrations, and the other two states adjust the damping and frequency response of the mount.
Neither an engine mount nor vacuum actuated switching of the states in an engine mount is individually deemed novel per se. However, a need exists for an improved switchable inertia track assembly and associated method of packaging same.